These studies should provide insight into the mechanism of the regulation of protein synthesis in higher organisms. The his4 gene cluster in yeast will be investigated to see if it is like a bacterial operon. The enzyme aggregate produced by this region carries out three steps in the pathway. Chemical studies should provide evidence whether the aggregate is more than one polypeptide. A protease which cleaves part of this complex will be studied. Several methods for obtaining mutants of this proteolytic enzyme are suggested. It should be possible to determine what role if any this protease plays in protein synthesis and regulation. Experiments are designed to test whether the gene for the first enzyme in the pathway has a heretofore unrecognized role in the genetic regulation of the pathway examined. Since no nonsense mutations are found in the gene for the first enzyme (his1), it must have the information for some other vital function. Analysis of revertants of existing his1 mutants whould provide one clue as to the hidden function. A second approach is the study of a mutant which excretes histidine into the medium. This mutation which maps in the gene for the first enzyme appears to affect the genetic regulation of the histidine pathway. The genetic organization of vital functions on yeast chromosome will be studied using disomics. Our technique should enable us to saturate a chromosome with temperature sensitive mutations. Subsequently, these temperature sensitives will be analyzed for the biochemical consequences. This should provide some insight into the relationship between gene location and gene function in eucaryotes.